Arthrosis, or osteoarthritis, is a very common joint disorder which tends to worsen with time.
Onset occurs when, for a variety of reasons, the articular cartilage is no longer able to resist the continuous stresses during the movement of the limbs.
The insufficiency of the cartilage may be due to age, excess weight which overloads the joint, hereditary factors or environmental factors (climate, etc.).
The joints most frequently affected are the hip, the knee, the vertebral column and all joints affected by former injuries; symptoms are initially mild and often intermittent.
Pain is characteristic: in the morning it is intense, improving during the day and becoming worse again towards the evening. As the disease progresses, pain becomes continual.
Another symptom is the reduction in movement which may even lead to immobilisation.
The probability of developing more or less serious forms of arthritis occurs in particular in subjects with varus or valgus deformity of the knee. In these subjects, especially when elderly, the cartilage of the knee joint becomes worn and the joint is chronically or acutely inflamed.
A specific brace for a knee affected by arthrosis must first of all be capable of enveloping the joint, following the individual conformation of the limb, and of providing medial or lateral thrust which opposes the pathological unbalancing of the load.
This can be achieved by applying, for example, pressure which alters the contact between the opposite condyles of the knee bone, reducing the pressure on the condyles and limiting the pain.
Some solutions known to background art foresee the use of flexible hinges which are fitted to the side arms of the structure, making it possible to adjust the brace at the joint both laterally and medially.
For example, the document U.S. Pat. No. 5,400,806 describes a brace with a hinge positioned on the side part of the structure at the level of the joint, capable of tilting the femoral and tibial arms of the side upright at a certain angle, thus applying a force perpendicular to the axis of the leg.
The document WO-A-97/40789 presents another example of a brace with angular compensation hinges which can be adjusted to modify the medial or lateral thrust force exerted by the brace at the knee joint.
The technical solution described is not without disadvantages, the first being the fact that the angular stress exerted by the hinges fitted to the structure of the brace is concentrated on the joint which allows movement of the femur with respect to the tibia, making it particularly delicate from a mechanical point of view.
Furthermore, the side upright is completely rigid, excluding the use of a second upright in the structure of the brace as the normal variations in knee volume during walking would cause the knee to be compressed.
On the other hand, the use of two uprights in structures of this type of brace is usually preferred due to the stability and control that they provide.
The document WO-A-01/45600 describes a brace with a hinged joint structure which comprises a part supporting the joint, a first gear portion supported during rotation, in relation to the part supporting the joint and with gear teeth on one portion. The first gear portion is coupled by rotation to the upper support arm of the brace and has a joint surface adjacent to the surface of the support arm.
A second portion of the gear, also supported during rotation by the same support part and having the same structure as the first portion, is coupled by rotation to the lower arm of the brace.
The joint surfaces of the first and second gear portion as described in WO-A-01/45600 are configured in such a way as to allow a predetermined medial/lateral articulation angle of the upper and lower arms, keeping the two portions of the gear on the same plane.
One upright also presents hinges which can be micrometrically adjusted to allow tilting of the upper and lower arms of the upright leading to a perpendicular thrust force on the limb axis.
The main disadvantages of the brace described in WO-A-01/45600 concern the overall dimensions of this hinged joint at the sides of the brace, since the curvature of the limbs in subjects with osteoarthritis is already particularly accentuated and can even be problematic in those with valgus deformity of the knee.
The system which connects the uprights to the central joint and the two parts presenting the gear teeth are also particularly delicate and easily subject to seizure since most of the force exerted by the joint during walking is concentrated on these parts and because they present a considerably extensive interconnecting and friction surface.
Finally, the uprights are rigid and cannot adapt to the anatomical structure of the limb and of the knee joint, nor to its physiological variations in volume during walking, this effect being particularly negative with the flexion between the femur and the tibia causing compression of the knee, less fluid movements and consequently less steady walking.